Alpha Magnetic Spectrometer zeroes in on dark matter

The Alpha Magnetic Spectrometer (AMS) surveys the sky for high-energy particles, or cosmic rays. It has seen evidence for what could be dark matter colliding with itself in a process known as "annihilation".

But scientists stress that a precise description of this enigmatic cosmic constituent is still some way off. "It could take a few more years," said AMS deputy spokesman Roberto Battiston, a professor of physics at the University of Perugia, Italy.

"But the accuracy that AMS is displaying is far greater than past experiments, so we're getting closer to unveiling the cause of the particle events we're detecting," he told BBC News. Dark matter accounts for most of the mass in the Universe.

It cannot be seen directly with telescopes, but astronomers know it to be out there because of the gravitational effects it has on the matter we can see. Galaxies, for example, could not rotate the way they do and hold their shape without the presence of dark matter.

AMS - a particle physics machine nicknamed the "Space LHC" in reference to the Large Hadron Collider here on Earth - has been hunting for some indirect measures of dark matter's properties.

It counts the numbers of electrons and their anti-matter counterparts - known as positrons - falling on to a battery of detectors.